Where Ixodes dammini is the vector of the Lyme disease spirochete (Borrelia burgdorferi), exposure to infected nymphal ticks (= entomologic risk) is perhaps the most important factor affecting the risk for transmission. The overall goal of this proposed study is to identify the source(s) of B. burgdorferi infection in vector ticks and to characterize those ecological conditions either promoting or inhibiting infection of the tick population. Characteristics of several sites described by varying degrees of entomologic risk will be assessed. The parameters to be evaluated will include: the relative abundance or absence of certain vertebrate hosts, the level of zoonotic infection, rates of zoonotic inoculation, and other physical descriptors of the habitat. In addition, the rate at which spirochetal infection develops in newly established tick populations will be measured. It is expected that one or more of the parameters contributing to the abundance of infected ticks and thus, risk for transmission, will have some predictive value in eventually assessing the human and animal risk for acquiring this infection.